1. Field of the Invention
This invention relates to a process for producing oil-soluble polyol ester derivatives of a dicarboxylic acid material under conditions of reduced filtration suppressing insolubles formation as well as to the resulting substantially insolubles-free product solution useful for preparing ashless dispersants utilized in lubricating oil and fuel compositions. In particular, this invention is directed to an insolubles-free solution process involving the polyol esterification of alkenyl succinic anhydride preferably poly(isobutenyl) succinic anhydride to provide lubricating oil and fuel additives wherein said reaction is carried out in the presence of an insolubles-reducing amount of an oil-soluble metal salt of a hydroxy aromatic compound.
2. Description of the Prior Art
During the past several decades, ashless sludge dispersants have become increasingly important, primarily in improving the performance of lubricants in keeping the engine clean of deposits and permitting extended crankcase oil drain periods while avoiding the undesirable environmental impact of the earlier used metal-containing additives. Most commercial ashless dispersants fall into several general categories.
One category of ashless dispersants involves the esterification product of alkenyl substituted acids, e.g. polyisobutenyl succinic acids, with polyols, e.g. pentaerythritol, as taught in U.S. Pat. No. 3,381,022; however, the usual process of making such a dispersant requires not only an esterification catalyst (such as sulfuric acid, benzene sulfonic acid, p-toluene sulfonic acid, phosphoric acid, etc., see col. 5, lines 68-75) but must be carried out at such an elevated temperature that large amounts, i.e. in the range of 2 to 6 vol.%, of insolubles are formed.
One approach to removal of the resulting insolubles, stated to be unconverted, insoluble pentaerythritol, is to conduct the esterification in the presence of a pyridine base which functions both to reduce the buildup of sublimates by its dissolution and as an entrainer to remove the unwanted by-products of the esterification (see U.S. Pat. No. 4,199,553). Unfortunately, this approach requires subsequent removal of the pyridine base with its environmental and extra process cost parameters, a long esterification time and introduces an insoluble phase which suppresses filtration of the product including an increase of filtration time.